1. Field of the Invention
The present invention relates to a position detector used in various information terminals, and the like, requiring a touch input performed with a finger and a stylus pen.
2. Description of the Related Art
In order to enhance a man-machine interface, information terminals that enable performance of a touch input, such as a touch panel and a tablet, have already been on the market. Position detectors are used as means for embodying a touch input. A position detector generally detects a position on a surface of a panel, or the like, touched with a finger or a stylus pen (hereinafter often called a “position pointing member”). The thus-detected contact position is converted into predetermined positional information, and the information terminal is configured so as to carry out various processing in accordance with the positional information.
A configuration for detecting a position contacted with a position pointing member described in connection with; for instance, (Patent Document 1) is a position detector that detects a change in electrostatic capacitance occurring when the position pointing member is pressed against a surface of a panel, or the like.
A position detector described in connection with (Patent Document 1) has a multilayered structure. Specifically, a plurality of electrodes (a first electrode group) are formed on one side of a sheet having a predetermined dielectric constant so as to run parallel to each other. Another plurality of electrodes (a second electrode group) are formed on the other side of the sheet so as to cross the first electrode group and run parallel to each other (the electrode groups or a single electrode is sometimes collectively referred to as “detection electrodes”). Both sides of the sheet having the thus-formed detection electrodes are sandwiched between sheet-like substrates, to thus make the multilayered structure. The structure makes it possible to detect a position contacted with a position pointing member with high accuracy.
Patent Document 1: U.S. Pat. No. 4,686,332
For instance, in a position detector utilizing a change in electrostatic capacitance described in connection with (Patent Document 1), a change in electrostatic capacitance occurring as a result of a position pointing member contacting a panel surface is taken as ΔC. Further, electrostatic capacitance determined by combined capacitance of adjacent electrodes, among electrodes running parallel to each other, achieved without regard to presence or absence of the contact of the position pointing member is taken as C. In order to stably detect a change in electrostatic capacitance resultant from a contact of the position pointing member with high accuracy, it is desirable to minimize the electrostatic capacitance C and increase ΔC that is an amount of relative change in electrostatic capacitance.
However, when a related-art position detector utilizing change in electrostatic capacitance is applied to a large-size display panel measuring 100 inches, or thereabouts, a length over which detection electrodes run along with each other in a detection panel making up the position detector exceeds 1000 mm. Interline capacitance arising between adjacent detection electrodes eventually increases, and the number of crosses (the area of crosses) between the first electrode group and the second electrode group also eventually increases.
More specifically, when a large-size detection panel measuring 100 inches is built, electrostatic capacitance of one detection electrode closely reaches 100 pF. On the contrary, changes in electrostatic capacitance induced by a contact of the position pointing member; namely, ΔC1 and ΔC2, usually come to only 1 pF or less.
In short, the electrostatic capacitance C achieved even when the position pointing member is not held in contact with the panel is large, whilst ΔC arising when the position pointing member is brought into contact with the panel becomes relatively smaller. Thus, the large-size panel encounters a problem of being susceptible to influence of external noise and difficult to stably detect a position with high accuracy.